This invention relates to a method for the manufacture of a silicon oxide-based insulation film and an interface possessing stable electric properties between the insulation film and a semiconductor.
Heretofore, for the purpose of immobilizing the movable ions in the silicon dioxide (SiO.sub.2) constituting the insulation film and consequently stabilizing the electric properties of the insulation film, there has been generally adopted a method which involves subjecting the SiO.sub.2 film to a thermal treatment in an atmosphere containing phosphoric oxide at an elevated temperature thereby forming a phosphorus glass layer on the surface thereof and gettering the movable ions or subjecting the SiO.sub.2 film to thermal oxidation in an atmosphere containing chlorine or hydrogen chloride thereby introducing into the SiO.sub.2 film chlorine atoms as a barrier to the movable ions. It has been further known that this oxidation in the atmosphere containing chlorine is effective in lowering the value of the interface state density between SiO.sub.2 and Si, decreasing the dispersion of the dielectric strength of the SiO.sub.2 film (although, the decrease cannot necessarily be expected to bring about an increase in the value of dielectric strength) and reducing the crystalline defects in the Si surface. Since the radius of the atom of chlorine is larger than that of the atom of Si, however, it is difficult for the oxidation to fill completely the defects within the SiO.sub.2 film or those in the Si surface. In contrast, hydrogen possesses a smaller atomic radius and, therefore, proves advantageous for the purpose of filling such defects and, actually, is effective in this respect. It nevertheless has a disadvantage that it effuses when SiO.sub.2 --Si system is heated to temperatures of 300.degree. to 400.degree. C. and it readily yields to electronic state change under the influence of a high-energy carrier, an electron beam or an ultraviolet ray which is transferred to the SiO.sub.2 film and the SiO.sub.2 --Si interface. The inventors' attention was attracted by the fact that fluorine, which is a monovalent element having a smaller atomic radius than Si, is effective in enhancing the stability and quality of the SiO.sub.2 film and the interface between SiO.sub.2 and Si. It has been known, on the other hand, that the fluorine ion dissolves SiO.sub.2 and, worse still, corrodes quartz reaction tubes generally adopted for thermal oxidation and other similar reactions.